Interesting that you don't think castor is needed on the Norvels. I usually put 3 oz. in most to my purchased fuels. I really am not a believer in castor, but use it anyway ;-) Anyway, the reason Sig fuels may work better than your other mixtures may be because the nitro is often shipped with a 50 - 50 mix of methanol because of regulations. Depending on sources, this may not be figured into the mixture? Possibly.